1. Field of the Invention
The invention relates to a method and an apparatus for cleaning surfaces, in particular sensitive surfaces, which are contaminated by environmental influences. The method described here is a further development of the cleaning method for surfaces according to European patent no. 0 171 448.
2. Description of the Prior Art
In the aforementioned patent specification several substances are mentioned as suitable blast material, that is in particular sharp-edged blast material such as sand (a silicon compound), quartz, corundum, or flue ash. These blast materials are united in the form of a blast material/air jet in a mixing head with an air/water jet to form a total jet disposed in inherent rotation. The atomized total jet emerging from the mixing head is directed onto the surface to be cleaned, said total jet rotating about its centre axis and being similar to a cone diverging in the jet propagation direction.
Since, in particular with highly sensitive surfaces the aforementioned sharp-edged blast materials can lead to removal of surface layers and thus to damaging of the surfaces, it is proposed in European patent application no. 88 121 432.4 to employ blast materials of low hardness, i.e. a hardness which as a rule is less than the hardness of the materials to be cleaned, so that although the dirt or contaminating layers are satisfactorily removed the material surface to be cleaned cannot be destroyed. In the method described in this publication mineral blast materials are used which have a hardness (Mohs' hardness) of at the most 4, as is the case with dolomite, which is specified as preferred rock-forming mineral. However, in many cases this method makes a subsequent washing of the cleaned surfaces necessary and also presents the problem that the mineral blast material, for example dolomite dust, can get into waste water and cause considerable problems there.